1. Field of the Invention
The present invention relates to a display device and more particularly relates to a liquid crystal display device allowing to maintain a contrast without increasing power consumption even under a light environment.
2. Description of the Related Art
In the liquid crystal display device, a TFT substrate on which pixels having pixel electrodes and thin film transistors (TFT) are arranged in a matrix and a counter substrate on which color filters and the like are formed at places corresponding to the pixel electrodes of the TFT substrate are arranged in opposition to each other, and a liquid crystal is nipped and held between the TFT substrate and the counter substrate. Then, an image is formed by controlling transmittance of light through liquid crystal molecules pixel by pixel.
Since the liquid crystal display device is made thin and light-weighted, it is used in a cell phone, a DSD (Digital Still Camera) and others. The cell phone and the DSC are frequently used in the light open air. When the cell phone or the like is to be used in the light open air, the contrast becomes a problem. If the brightness of backlight is increased in order to create a visible contrast, its power consumption will become a problem.
As related art taking measures to a relationship between the power consumption and the contrast, the followings may be given. (1) One system is such that the contrast of a light room is maintained by sensing the illuminance of outdoor light in an environment that a display is used without increasing the power consumption. That is, in this system, while when the outdoor light is light, the power of the backlight is increased, when the outdoor light is dark, the entire power consumption is saved by decreasing the power of the backlight. (2) Another system is such that the power of the backlight is decreased by combining it with backlight control on a menu screen or the like which is little in color information. However, also in this case, input image data is used as it is. (3) A further system is such that a white pixel (W) is added to a red pixel (R), a green pixel (G) and a blue pixel (B) so as to increase the luminance though the color purity is slightly sacrificed.
In addition to systems as mentioned above, a configuration that a first color filter which is excellent in color purity and a second color filter which is higher in transmittance than the first color filter are arranged side by side and the first color filter and the second color filter are separately controlled so as to flexibly cope with various external environments is described in Japanese Patent Application Laid-Open No. 2008-287068.